This invention relates to a spatially distributed routing switch.
The AES3 (AES standard for digital audio engineering-serial transmission format for two-channel linearly represented digital audio data) serial data stream developed by the Audio Engineering Society is composed of frames. Each AES3 frame represents one two-channel audio sample and is composed of two subframes, each of 32 bits. The sample rate is typically 48 kHz or 96 kHz (corresponding to sample periods of about 20 μs and about 10 μs respectively) and sample rates as high as 192 kHz (about 5 μs) are becoming more common.
U.S. patent application Ser. No. 09/661,844 discloses a routing switch designed for routing signals encoded as AES3 serial data streams. The routing switch comprises multiple routers each having a plurality of signal inputs, a plurality of signal outputs, an expansion input, an expansion output, and a switch core for selectively routing a signal received at any one of the signal inputs to any one or more of the outputs and for routing a signal received at the expansion input to any one or more of the signal outputs. The expansion output of each router is connected to the expansion inputs of the other routers. Consequently, each input signal of each router is available to each output of each router.
In a proposed implementation of the routing switch described in patent application Ser. No. 09/661,844, each router has 256 signal inputs, each receiving a signal encoded as an AES3 serial data stream, and is composed of four router modules each having 64 signal outputs, so that the router serves a total of 256 signal outputs. In general, fewer than 256 of the data streams received at the signal inputs of the router module will convey information that is to be routed to a signal output of the router, and the data streams that do not convey useful information may be AES3 silence.
In the proposed implementation of the routing switch, the 256 data streams received at the signal inputs of each router are supplied to the expansion output of the router in time interleaved format. The composite data stream received at the expansion input of a router, i.e. the data stream composed of multiple AES3 data streams, is demultiplexed and a selected data stream may be routed to any signal output of the router.
In an application of the routing switch, input data streams received at signal inputs of two or more routers may be used to create an audio image of multiple data streams outputted by one of the routers. In order for the output data streams to be image accurate, the input data streams must have the same sample rate and the sample clocks must be aligned in time to within less than one sample period. Loss of time alignment by as little as one sample period (about 10 μs for a 96 kHz sample rate) can lead to perceptible degradation of the audio image. When the several routers are in relatively close physical proximity (e.g closer than 100 m), it is possible to use a common master clock and cables of equal length to ensure that the sample clocks are of the same frequency and are time aligned across the signal sources.
The global positioning system (GPS) employs a constellation of satellites orbiting the earth and each emitting a signal coded in accordance with a pseudo random digital code. The pseudo random code signal allows two terrestrial GPS receivers, no matter their relative positions, to measure lapse of time relative to a common time origin with a precision of 1 ns.